The present invention relates to a device and a method for controlling a brake for a drilling rig, and to an automatic drilling system implementing such a device.
The invention relates more particularly to the field of petroleum drilling of the “rotary table” type and/or of the “top drive” type. A “rotary table” system usually includes an injection head, a pull rod or kelly that passes through a rotary table and that is connected to a string of drill-pipes or “drill string”, and, at the end of the string, a drill tool or “drill bit” that cuts into the ground. The kelly, and therefore the drill string and the drill tool at the end of the string are all subjected to rotation via the rotary table and via an angular section of the string that is situated at the table, or, if the table does not constitute the means for rotating the drilling machinery, via the injection head that also serves to drive the string. The invention could also be applied to the field of geothermal drilling.
On a drilling rig, the drill string, which, at its bottom end, is provided with the drill tool, is hooked onto a drill hook, movement of which is controlled by a drilling draw-works or winch. The drilling draw-works includes a brake for preventing the cable from unwinding from the draw-works in an untimely manner. The operator or “driller” uses a device referred to as a “brake control” for controlling loads or tools lowered into the borehole or “well”. The brake control thus makes it possible to control the speed and deceleration of the drill hook, optionally to the extent of stopping it from moving.
On a majority of drilling rigs, the brake is a mechanical brake having bands. Such a brake is made up of two metal bands equipped with internal linings fastened by flush-head or “countersunk-head” copper or aluminum bolts. Those bands are connected together by a balancing bar that also distributes the braking force between the two bands, thereby reducing the wear on the brake shoes or “brake pads”. Each band wraps around a respective rim constrained to rotate with the drum. One end of each band is stationary, while the other end is connected via a set of cams and connection rods to a hinged lever (the brake control), thereby making it possible to gear down the force to be exerted on its end.
On other drilling rigs, the brake is a disk brake. In which case, the brake control is implemented in the form of a joystick.
Whether it be via use of a brake control in the form of a hinged lever or “brake lever”, or in the form of a disk brake, manual control of the brake control by the driller can give rise to lack of accuracy in actuation of the brake control, which can lead to under-efficiency of the progress of the drilling and to premature wear on the drill tool. An error by the driller can lead to the drill tool being destroyed, or to the well being lost.
Since the constitution of the ground varies over any given drilling stage, manual control of a brake control requires constant attention, which, for example, constitutes a safety problem due to the human factor. An object of the invention is thus to propose a device and a system, as well as a method, for automating the brake control.
Document U.S. Pat. No. 4,187,546 discloses a drum brake including a primary brake whose function is to control the speed and the deceleration of a traveling block of the draw-works, and to stop it from moving. That primary brake is a drum brake that can be actuated manually via a brake control. In addition, that document discloses a return spring that urges the drum brake back into the braking position. That document teaches that the spring can be overridden manually so as to release the brake. It discloses that the lever may be connected to a brake actuator comprising a cylinder provided with a piston. Injecting fluid into the cylinder moves the piston, thereby causing the brake control to move to modulate the force on the brake. The force exerted by the piston on the brake control must exceed the return force of the spring. Emergency braking takes place by emptying the fluid contained in the cylinder into the atmosphere, thereby causing the piston to descend into the cylinder and then the brake control to be urged back by the return spring. It should be noted that such emptying of the fluid contained in the cylinder can give rise to risks of pollution and can be toxic.
Document EP 0 694 114 also discloses a primary brake in the form of a band brake that is, a priori, manually actuatable by a brake control. That document discloses an additional return spring that urges the band brake into the braking position and that can be overridden manually for releasing the brake. The lever may be connected to a brake actuator assembly. More precisely that brake actuator assembly comprises a lift unit connected to a lift line or cable for pulling on the end of the brake control to modulate the force on the brake. Thus, the function of the lift unit is to oppose the return force of the spring and thus to allow the drilling draw-works to descend. For this purpose, the force exerted by the lift unit on the brake control must exceed the return force exerted by the spring on the brake control.
A first drawback with such brake devices is that they have reactivity characteristics that are difficult to make compatible with the numerous variations in the ground that can require very quick reactions, such as when drilling through an influx or encroachment of fluid in the borehole requiring almost instantaneous stopping. In addition, if the spring breaks, the drill hook and its load descend unbraked, with disaster ensuing.
Another drawback with such devices is that the additional spring is dimensioned to exert a return force that is sufficient to withstand the maximum weight that is implemented when the drilling is at its deepest possible. This implies that the largest force for countering that return force and for allowing the brake to descend is implemented at the start of drilling. That implies forces that are very high in the early stages of drilling. The deeper the borehole and the drilling become, the lower the force necessary for releasing the brake. That can give rise to safety problems for very deep drilling.
Another drawback with such devices is that they require the brake control to be equipped with more than one instrument. Unfortunately, a control cabin for a driller is often a very confined space. An object of the invention is thus to propose a device that is more compact than the prior art devices. Another object of the invention is to propose a brake actuator device that is faster, more accurate, and safer during braking and more particularly during emergency braking.
Another problem-solving object of the invention is to install a device that is transparent when used by the site manager, i.e., that requires less learning by the site manager about how the device operates. Another problem-solving object of the invention is to propose a device arranged to operate in co-operation with the driller.